Vented duplex tube assembly



Sept. 8, 1970 1.. A. MEISSE ETAL 3,527,293

VENTED DUPLEX TUBE ASSEMBLY Filed Nov. 13, 1968 w 0% 3 M 61 0 Z 2f A 1 a M /1 .mvruwww QEN mumvwtmv k WW United States Patent O 3,527,293 VENTED DUPLEX TUBE ASSEMBLY Louis A. Meisse, Jamestown, N.Y., and Gary Lloyd,

Wheaton, 111., assignors to Plymouth Tube Division of Van Pelt Corporation, Bloomingdale, 11]., a corporation of Michigan Filed Nov. 13, 1968, Ser. No. 775,408 Int. Cl. F28f 1/36 U.S. Cl. 165ll78 4 Claims ABSTRACT OF THE DISCLOSURE A vented duplex tube assembly comprised of an inner metal tube, and an outer metal tube, said metal tubes being of dissimilar materials and being in generally telescoped position relative to one another, said duplex tube containing at least one or more wires located between the inner and outer metal tubes, said wire serving the function of permitting the venting of gas from between the tubular portions.

BACKGROUND OF THE INVENTION This invention broadly relates to a tube assembly and method of using same. More particularly the invention relates to a vented duplex tube assembly suitable for use in a heat exchanger or the ilke.

The state of the prior art patents known to the applicant is generally indicated in the following US. patents: Pels et al. 3,123,133 and Heith 3,330,337.

In the past, vented duplex tubes (two tubes in generally telescoped position relative to one another) have been used in heat exchangers wherein one particular heat exchanging fluid passes through the interior of the vented duplex tube and a second heat exchanging fluid passes over the outside of the duplex tube. These two heat exchanging fluids being of different physical and chemical characteristics generally require that the two metal tubes, which normally make up the basic construction of the duplex tube, must be of different materials in order to satisfactorily fulfill different corrosion characteristics, etc. Due to the fact that the metal tubes which make up the duplex tube are of different materials, there is a different degree of thermal expansion between the two tubes when the assembly is actually used in operation.

When the heat exchanging fluids are passed through and over the tube assembly, it is conventional for certain gases to be produced and these gases diffuse through the telescoped tubes such that there is normally at least a certain amount of the gases which collects between the opposing surfaces of the two tubes and this gas then attempts to pass therebetween along the length of the tube.

Unless provision is made for the escape of these gases from between the two telescoped tubes, then there is a serious problem and detrimental likelihood that the buildup of pressurized gas between the two tubes will cause distortion, buckling, or even physical breakage of the duplex tube construction. It has been conventional in the past to attempt to solve this problem by placing certain forms of layers which are permeable to the passage of the gas between the two tubes. In Pels et al. the problem was attempted to be solved by wrapping sandpaper around the two ends of the inner tube such that a layer would be provided between the tubes allowing for the escape of gas. However, such use of sandpaper or other hard particles as disclosed in Pels et al. has not been found fully satisfactory for the reason that the telescoped tubes still bind together at portions intermediate the ends thereof, such that the buildup of gas would not be prevented, thereby often leading to subsequent damage of the duplex tubes.

Still another problem with the Pels et al. construction is that during the rolling in operation to seal the tube ends into the tube sheet, that is in forming the heat exchanger, the rolling pressure inside the tube is sufficient to cause at least one of the tubes to conform to the grains of the sand, thereby effectively sealing the interface between the tubes which in eifect prevents the escape of the gas from between the tubes.

Accordingly, in view of the above, it is a primary object of this invention to provide an improved vented duplex tube assembly.

Another broad object of the invention is to provide an improved tube assembly.

Still another object of the present invention is to provide an improved tube assembly comprised of at least one inner tubular portion and at least one outer tubular portion in generally telescoped position relative to one another, wherein at least one piece of wire is located between the inner and outer tubular portions, with the wire extending the length of the tube assembly such that pressurized gas which collects at any point along the tube assembly is permitted to be vented therefrom.

Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a vented duplex tube in accordance with the invention wherein at least one piece of wire is positioned between telescoped tubes and generally extending the length thereof; and

FIG. 2 illustrates a cross-sectional view along the line 2--2 of FIG. 1.

SUMMARY OF THE INVENTION It has now been discovered that an unexpected and unique solution to the problem of sensitivity to the rolling in pressures mentioned above, while retaining the heat transfer capability, is accomplished if one or more small diameter wires are embedded in or positioned between the inner and outer metal tubes. Moreover, during the preparation of the duplex tubes disclosed here in which the rolling pressures or contact pressures are limited to the deformation stresses in the materials, longitudinal channels are formed on both sides of the wire and these channels permit for the escape of the gases which are caught between the two tubes. Still further, during the rolling in operation which comprises: (a) a circular expansion of the tube end into the hole in the tube sheet forming part of the heat exchanger, and (b) then a further cold working with consequent extrusion of the tube material; the existence of small gaps adjacent to the wire in the interface has a maximum dimension radial to the tube and tangent to the wire. The orientation of this gap is very unfavorable to the plastic flow of the tube material and therefore the capillary channel or longitudinal channel formed will persist even under the most severe rolling operations.

Briefly stated therefore, the present invention comprises a tube assembly for use as a duplex tube or the like, said tube assembly being comprised of: at least one inner tubular portion, at least one outer tubular portion, said inner and outer tubular portions being generally telescoped together, wire means located generally between said inner and outer tubular portions, for permitting venting of gas from between the tubular portions, said wire having a diameter between about 1 mil and about 0.3 inch. More particularly, said wire means may be comprised of at least one piece of wire positioned between the inner tubular portion, and the outer tubular portion, and this positioning may be in a generally straight through or in a helical fashion.

From a method aspect, briefly stated, the present invention comprises a method of using the tube assembly disclosed herein by positioning at least one of said tube assemblies in a heat exchanger and subsequently passing a first fluid across an outer surface of the tube assembly and a second fluid inside and through the tube assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS FIGS. 1 and 2 show a vented duplex tube generally designated comprised of an inner metal tube 12 and an outer metal tube 14, with the two tubes 12 and 14 usually being of dissimilar metals.

As an illustrative example, the inner tube 12 may be made of brass and the outer tube 14 of a steel or ferrous alloy. The gas which collects between the two tubes 12 and 14 is generally collected at a. position between the opposed surfaces of the two tubes with this point of collection being designated 16 in the drawings.

A wire means or wire separator 20 is shown positioned helically around the inner tube 12 such that the wire 20 is positioned between the two tubes 12 and 14. This separator wire 20 serves the purpose of permitting the buildup of gases such as hydrogen gas or the like, to be vented from the interface or space 16 between the inner and outer tubes 12 and 14 respectively. The discovery has been made herein that a wire separator means such as that designated 20 provides an excellent and unique manner of venting the collected gases which form at the general points designated 16 between the tubes 12 and 14. It has also been found that when the duplex tube in accordance with this invention is manufactured in a conventional manner, which usually involves compressing the tubes 12 and 14 together, that this does not seal off the interface 16 between the tubes 12 and 14 in the areas closely adjacent the wire 20 and for this reason the collected gases are still permitted to be vented from between the two tubes. Furthermore, while there may be a certain amount of imbedding or flattening of the wire 20 between the tubes 12 and 14 during the manufacture of the vented duplex tube disclosed herein, this minor degree of imbedding or flattening does not seal off the generally longitudinal escape passage or channels 99 and 99a (FIG. 2) formed immediately adjacent the wire and therefore the gases collected between the two tubes 12 and 14 are permitted to escape.

The ends of the metal tubes 12 and 14 may be coextensive in length or as an alternative, the end designated 12a of the inner metal tube 12 may extend beyond the tube 14. A gas permeable metal sleeve or ferrule may be slidably fitted over the end portion 12a with said sleeve serving the purpose of further facilitating the venting of gas from between the tubes 12 and 14 when the tube assembly disclosed herein is used in a heat exchanger. Such gas permeable metal sleeves are known in the art and per se form no specific part of the present invention.

The thickness of the wire used in accordance with the above disclosure should broadly be within the range of about 1 mil to about 0.3 inch. However, preferred results in accordance with this invention are obtained when the wire thickness is within the range of about 2 up to about mils; and, best results are obtained when this wire thickness is within the range of about 4 to about 8 mils.

It should be understood that the drawing of the vented duplex tube disclosed herein and the wire which is disposed therebetween is not drawn to scale and that the invention herein is applicable to any size of tube assembly regardless of whether the tube assembly is relatively large or relatively small in size.

While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

Still further, while the advantages of this invention should be apparent from the disclosure hereinabove, it is specifically stated at this point that a particularly important advantage of this invention is that the wire separator 20 or wire venting means extends substantially throughout the length of the duplex tube and therefore is less susceptible to being negated, that is sealed off, during the tube rolling or expanding operation. Furthermore, this advantage is particularly operative and effective during actual usage of the tube assembly of this invention.

What is claimed is:

1. A tube assembly, for use as a duplex tube in heat exchangers or the like, said tube assembly being comprised of:

at least one inner tubular portion,

at least one outer tubular portion,

said inner and outer tubular portions being generally telescoped together,

wire means, located generally between said inner and outer tubular portions, for permitting venting of gas from between the tubular portions,

said wire having a diameter between about 1 mil and about 15 mils, said wire means being accommodated between the inner and outer tubular portions such that the wire means is generally positioned between said portions in tight fitting relationship and generally leaving a small space contiguous with said wire means for the escape of gas.

2. The tube assembly of claim 1 wherein said diameter is between about 4 and about 8 mils.

3. The tube assembly of claim 1 wherein said wire means is comprised of at least one piece of wire positioned in helical fashion around the inner tubular portion.

4. The tube assembly of claim 2 further characterized in that i said inner tubular portion has an end which protrudes beyond said outer tubular portion, and including a gas permeable metal sleeve means positioned on said end of the inner tubular portion for further facilitating the venting of gas from between the tubular portions.

References Cited UNITED STATES PATENTS 2/1962 Peeps et al. -l56 7/1967 Heith 165-178 1 U.S. Cl. X.R. l3838 

